1. Field of the Invention
This invention relates to the field of switching systems for communication networks.
2. Prior Art
There are many commercially available computerized branch exchanges used for the switching of voice signals as well as data signals. A common feature of these systems is the conversion of analog signals to digital and the transmission of such digital voice signals and digital data signals over a common bus. One such system is described in U.S. patent application Ser. No. 613,026 for "Time Division Multiplexed Computerized Branch Exchange," filed May 22, 1984.
A disadvantage of prior art switching systems is the utilization of centralized control capacity. A switching system utilizes a Time Division Multiplexed (TDM) bus divided into time slots which are assigned to various stations by the central controller. Although the maximum capacity of the system may not be currently in use, the entire control system must be provided for. Such a system is inefficient for users and does not have flexibility beyond the capacity of the original control unit. In addition, prior art switching systems are not fault tolerant, if there is a failure in the controller, the entire system fails. Further, in order to modify the system once in place, the entire system must be shut down prior to making additions.
In addition, it is often desired to provide a switching system that is user configurable. For example, by programming at a system level, certain phone stations may be restricted from making long distance calls, programmed to emit coded tones depending on the type of incoming calls, etc. In prior art systems, such programming is lost upon the occurance of power failure or performance of maintenance on the system. Further, individual stations may be user configured form memory dialing, quick dial, etc. This individual programming may also be lost during system failures and maintenance operations.
Therefore, it is an object of the present invention to provide a switching system which does not require the provision of a large control unit for initial application.
It is a further object of the present invention to provide a fault tolerant switching system.
It is as yet another object of the present invention to provide a switching system which can be modified when it is in place without disturbing the system.
It is as another object of the present invention to provide a switching system in which system and station user configurations are retained during power down situations.